L-ornithine has been widely used as an ingredient of nutrition enriching additives, pharmaceuticals or the like.
Since it is difficult to prepare a free base of L-ornithine as crystals, it is available usually in the form of a salt such as hydrochloride (Product Catalogue 2004 to 2005 of Sigma).
When L-ornithine is used as an ingredient of a transfusion or the like for the purpose of nutrition enriching or the like, for example, by using it in the form of hydrochloride as it is, an acidosis symptom may be induced. Also, administration of a transfusion containing a large amount of chlorine ions is unfavorable for patients with a renal disease in particular. It has also been well known that when L-ornithine is used either by being mixed in foods or the like as a nutrition enriching additive or the like or orally as it is, it is difficult to utilize the same in the form of, for example, hydrochloride because of its bitter taste. Thus, there is a demand for L-ornithine as a free base. However, as described above, it is difficult to prepare L-ornithine crystals. In general, amorphous forms of amino acids are highly hygroscopic and are not preferred as distribution forms. Hence, there is a demand for L-ornithine crystals in a satisfactory distribution form and a process for producing the L-ornithine crystals.
Although use of an aqueous solution of free base of L-ornithine (aqueous L-ornithine solution) has already been known, a method for preparing L-ornithine crystals from the aqueous L-ornithine solution has not been known (see Patent Documents 1 to 3). It is known that an aqueous solution of free base of an amino acid including L-ornithine can thoroughly be dried to give crystals of the free base of amino acid. However, there is no specific description of L-ornithine crystals (see Patent Document 4).
Patent Document 1: Japanese Published Examined Patent Application No. 3194/1971
Patent Document 2: Japanese Published Unexamined Patent Application No. 364155/1992
Patent Document 3: Japanese Published Unexamined Patent Application No. 136254/1980
Patent Document 4: Japanese Published Unexamined Patent Application No. 144088/2003